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Why does a diving mask fog and what can you do about it?

Diving in South Africa doesn’t always offer the best of visibility. Depending on the time of the year and the location, sometimes seeing the magical underwater world beneath the waves is not as easy as you think. And when having to deal with a foggy diving mask, all of the excitement you’ve been feeling, all of the anticipation for the bright colours and open ocean you had expected to see, can be somewhat dampened.

When that fog starts making your dive unpleasant, you’ll probably be asking yourself “What the heck did I do wrong?”

After racking your brain for the reason why this has happened, it is likely that you would eventually resign yourself to the fate of a fogged up mask and an unhappy dive, but it doesn't have to be that way.

That Fog Mask

Every diver has been there. Remember, we were all amateurs at one time or another and we still have those bad days when we’ve done everything seemingly right, but ended up literally short of sight. No dive is completely ruined by a fogged up mask, but no one would say that this is the kind of dive we’ve been hoping for. Knowing why your mask has fogged up is actually a whole lot more important than simply fixing it. There are a few solutions to clearing up the fog, but not everyone knows why the mask is doing this in the first place. Knowing why it has fogged up can help you prevent future mishaps.

One of the biggest reasons why you suddenly have fog as you dive is condensation. All air, even the air in your mask, is full of water vapour. When there is lots of water vapour present in the air, we say the air is humid. When this water vapour cools down rapidly, something which will happen when you come into contact with the water, the vapour turns back into a liquid and fog up your mask.

You might want to argue this and say that the waters off the coast of South Africa, if you are diving in the Kwa-Zulu/Eastern Cape region, are actually warm. And you are correct but the water is not so warm that you won’t have a condensation issue.

This condensation, along with the fact that your mask is not actually perfectly made, leads to fog. There are small imperfections that you will not see, along with dust and dirt that is not visible to the eye, all within your mask. The now cooled water vapour will cling to this and as such, they will cause the mask to fog.

Even if you keep your mask religiously clean, there is a very good chance that soon after finishing up, invisible dust would have already settled there. There is nothing that can be done about this but there is something that you can do to remedy the foggy mask.

Getting rid of the fog

There are two great ways that you can get your mask cleared out. Firstly, you can warm the mask so that the condensation won’t occur in the first place. It might sound like a pretty straightforward solution, but when you actually think about it, warming up your mask is not exactly practical. Few divers have found an easy way to do this, or rather, an effective way to do this. So, in theory, you could rule this suggestion as something that can work but not in a practical sort of way.

Secondly, you can make sure that your mask is exceptionally smooth so that should condensation occur, it won’t stick to the mask and obscure your view. The way to do this is to make sure that the mask has nothing on which the condensation can stick. This is where the using spit or other slippery liquids is often coated on the inside of the mask. And it also explains why you will need to be very careful when rinsing your mask. Rinse too aggressively and you will end up creating scratches that will, in turn, allow condensation to build up.

By knowing what is causing your mask to fog, you are now in a better position to prepare for your dive in South Africa, safe in the knowledge that you mask will give you the clearest view.